CD4 and chronic obstructive pulmonary disease: CD4 + CD25 + Tregs have also been reported to induce the differentiation of M2 macrophages partially through the IL-10 and TGF-β pathways in a mouse model [30], a previous study showed that human CD4 + CD25+ Tregs could induce the differentiation of M2a and M2c macrophages [31], in which way CD4 + CD25 + Tregs and M2 macrophages mutually promote each other through positive feedback, leading to a strong anti-inflammatory environment that is beneficial for the treatment of COPD.